Immunological profiles of leprosy patients and healthy family contacts toward M. leprae antigens.

In this study, we measured simultaneously the in vitro and in vivo T lymphocyte reactivities and the antibody responses of leprosy patients and healthy family contacts (HFC) toward Mycobacterium leprae antigens. The in vitro lymphoproliferative response of the HFC to leprosin A was comparable to that of tuberculoid leprosy patients. However, their skin-test reactivity to Dharmendra lepromin was considerably higher compared to the in vitro response to leprosin A. A significant number of HFC failed to respond to M. leprae antigens, both in vitro and in vivo, and the unresponsiveness to either test was not related to the type of leprosy patients in the household. A marginal correlation was observed between the skin-test reactivity of HFC and the age of the individuals. Even though a significant proportion of HFC showed positive anti-PGL-I IgM levels, none showed a positive titer in the serum antibody competition test toward the M. leprae-specific epitope My2. A positive anti-PGL-I IgM response together with a negative lepromin skin-test reactivity showed a clear downward trend from the lepromatous pole toward the tuberculoid pole. A small number of HFC, all contacts of lepromatous patients, were lepromin skin-test negative with positive anti-PGL-I IgM levels, but the majority among them showed T-cell reactivity to mycobacterial antigens in vitro. These results are discussed in relation to immunological correlates of the susceptibility to M. leprae infection.